Light emitting keypad comprising light guide film and light guide

ABSTRACT

The present invention provides a light emitting keypad having a very slim light guide film, and a light guide film for a keypad backlight. Particularly, a reflection layer is formed on a lower portion of the light guide film, resulting in more improved luminance. According to the present invention, the introduction of an EL sheet is eliminated, substantial slimness is achieved as compared with a direct illumination type keypad, high luminance is obtained by introducing a reflection layer even though a small number of light sources are used, and a light emitting surface can be provided for intensive light emission onto key regions of a keypad by forming a predetermined pattern on at least one surface of the light guide film.

TECHNICAL FIELD

The present invention relates to a light guide film for a keypadbacklight and a light emitting keypad having the same.

BACKGROUND ART

In general, a light emitting keypad is applied to communicationequipment such as a mobile phone so that the light emitting keypad isused as a switch device for generating a signal or performing variousadditional functions. The light emitting keypad has the function ofenabling identification of numeral or character keys in the nighttime orat a dark place. Recently, an ultra-thin light emitting keypad has beendeveloped and employed as mobile phones become thinner.

FIG. 1 is a sectional view of a conventional direct illumination typeLED (Light Emitting Diode) keypad that comprises a printed circuit board(100), domes (102), direct illuminating LEDs (103), and a keypad portion(104). The printed circuit board (100) has contact terminals (101).Here, the plurality of domes and direct illuminating LEDs are installedon a front surface of the printed circuit board. The keypad potion thathas numerals or characters printed on an upper surface thereof andprotrusions (105) formed on a lower surface thereof is installed infront of the domes and the direct illuminating LEDs.

In this direct illumination type LED keypad, the keypad portion isilluminated by light emitted from the direct illuminating LEDs installedon the front surface of the printed circuit board. That is, when a userpresses a key of the keypad portion, a protrusion corresponding to thekey of the keypad portion allows a corresponding dome to be connected toa corresponding contact terminal of the printed circuit board togenerate a predetermined electrical signal. The generated electricalsignal causes a corresponding LED to emit light so that the keypadportion can be directly illuminated by the LED in the form of a pointlight source.

However, the aforementioned direct illumination type LED keypad ismanufactured to be relatively thicker since it is impossible tofabricate a thin keypad due to characteristics of the LEDs. Furthermore,the direct illumination type LED keypad may reduce a use time of abattery since power consumption increases according to light emission ofthe LEDs. Furthermore, there is difficulty in designing the directillumination type LED keypad since light emission uniformity may beirregular in accordance with the arrangement positions of the LEDs.

FIG. 2 is a sectional view of a conventional EL (Electroluminescence)type light emitting keypad for solving the aforementioned problems. TheEL type light emitting keypad comprises key tops (110), an EL metal domesheet (120) and a printed circuit board (130). The EL metal dome sheet(120) comprises an EL sheet (121), metal domes (123) and a base tape(122), thereby achieving ultra-slimness and low power consumption.

As for the function of this EL type metal dome keypad, when a userpresses the key top (110), a protrusion (111) disposed on a back surfaceof the key top (110) causes the metal dome (123) to be brought intocontact with a fixed contact terminal (131) of the printed circuit board(130) so that the keypad is switched on and operated.

However, in the conventional EL type light emitting keypad, there is ahigh risk that the EL sheet may be damaged or broken since the EL sheet(121) is consecutively pressed and impacted by the protrusion (111), andthus, a severe problem of degradation of the reliability of EL is causedand there is also a problem in that a click feeling of the keypad isdeteriorated. Furthermore, the conventional EL type light emittingkeypad has problems in that the EL sheet has a life span shorter thanthat of an LED due to characteristics of the EL sheet, noise is producedin an LCD module, and reliability is lowered. Moreover, the conventionalEL type light emitting keypad has a problem in that production costsincrease as compared with manufacture of an LED keypad.

DISCLOSURE OF INVENTION Technical Problem

In order to solve the aforementioned problems, it may be contemplatedthat an indirect illumination type LED light source is prepared and anoptical fiber with superior optical transmission characteristics foruniformly supplying light to a keypad is installed. However, since theoptical fiber is essentially made of silicone, there are problems thatit is difficult to make the optical fiber thin, and it is difficult toactually apply the optical fiber to the keypad.

The present invention is conceived to solve the problems in the priorart. An object of the present invention is to provide a light guide filmfor a keypad backlight, wherein substantial slimness is achieved ascompared with a direct illumination type keypad, the introduction of anEL sheet is eliminated to solve problems in an EL type keypad, highluminance is obtained by introducing a reflection layer even though asmall number of light sources are used, and a light emitting surface canbe provided for intensive light emission onto key regions of a keypad byforming a predetermined pattern on at least one surface of the lightguide film, and a light emitting keypad having the light guide film.

Technical Solution

The present invention for achieving the object provides a light emittingkeypad comprising a key plate with a plurality of keys formed thereon; aback layer disposed below the key plate and having a plurality ofprotrusions corresponding to all or some of the keys; a light guide filmformed below the back layer to cause incident light from a side lightsource to be surface-emitted; and a substrate disposed below the lightguide film and having dome switches formed at positions corresponding tothe positions of the protrusions, wherein the light guide film is a slimfilm with a thickness in a range of 50 to 250 μm.

Further, in the light emitting keypad of the present invention, areflection layer may be formed on a lower portion of the light guidefilm, and patterns may be locally formed in specific regions on at leastone of front and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad.

Moreover, the present invention provides a light emitting keypadcomprising a key plate with a plurality of keys formed thereon; a backlayer disposed below the key plate and having a plurality of protrusionscorresponding to all or some of the keys; a light guide film formedbelow the back layer to cause incident light from a side light source tobe surface-emitted; and a substrate disposed below the light guide filmand having dome switches formed at positions corresponding to thepositions of the protrusions, wherein a reflection layer is formed onall or a portion of an upper surface of the substrate having the domeswitches.

In the light emitting keypad, the light guide film may be a slim filmwith a thickness in a range of 50 to 250 μm, and patterns may be locallyformed in specific regions on at least one of front and back surfaces ofthe light guide film so that light is intensively supplied topredetermined regions of the keypad.

Furthermore, the present invention provides a light emitting keypadcomprising a key plate with a plurality of keys formed thereon; a lightguide film disposed below the key plate to cause incident light from aside light source to be surface-emitted; a plurality of protrusionsformed at predetermined positions below the light guide film; and asubstrate disposed below the protrusions and having dome switches formedat positions corresponding to the positions of the protrusions, whereinthe light guide film is a slim film with a thickness in a range of 50 to250 μm.

In the light emitting keypad, a reflection layer may be formed on alower portion of the light guide film, and patterns may be locallyformed in specific regions on at least one of front and back surfaces ofthe light guide film so that light is intensively supplied topredetermined regions of the keypad.

In the light emitting keypad, the light guide film may be made ofpolycarbonate (PC) or polyethylene terephthalate (PET).

In addition, the present invention provides a light guide film for akeypad backlight to cause incident light from a light source to besurface-emitted, wherein the light guide film comprises a reflectionlayer formed on a lower portion thereof, and patterns are locally formedin specific regions on at least one of front and back surfaces of thelight guide film so that light is intensively supplied to predeterminedregions of the keypad.

In the light guide film, the light guide film and the reflection layermay be spaced apart by a predetermined distance from each other.

In the light guide film, the light guide film may be a slim film with athickness in a range of 50 to 250 μm.

In the light guide film, the reflection layer may be formed of a sheetand attached to one side end, both side ends or the entire of the backsurface of the light guide film using a double-sided tape.

In the light guide film, the patterns may be formed by means of a hotpress method using a mold heated to a temperature in a range of 70 to150° C.

In the light guide film, the patterns may be formed by means of silkprinting using an ink containing a light-scattering material on thelight guide film.

In the light guide film, the patterns may have sizes increasing as thepatterns go away from the light source.

ADVANTAGEOUS EFFECTS

The present invention has the following advantages resulting from theaforementioned unique constitutions. That is, the present inventionprovides a light guide film for a keypad backlight, wherein substantialslimness is achieved as compared with a direct illumination type keypad,the introduction of an EL sheet is eliminated to solve problems in an ELtype keypad, high luminance is obtained by introducing a reflectionlayer even though a small number of light sources are used, and a lightemitting surface can be provided for intensive light emission onto keyregions of a keypad by forming a predetermined pattern on at least onesurface of the light guide film, and a light emitting keypad having thelight guide film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional direct illumination typeLED light emitting keypad.

FIG. 2 is a sectional view of a conventional EL type light emittingkeypad.

FIGS. 3 to 5 are sectional views of a light guide film according to anembodiment of the present invention.

FIGS. 6 and 7 are sectional views showing patterns of a light guide filmaccording to other embodiments of the present invention.

FIGS. 8 to 10 are plan views showing patterns of a light guide filmaccording to other embodiments of the present invention.

FIGS. 11 and 12 are sectional views of light emitting keypads havinglight guide films according to embodiments of the present invention.

FIG. 13 is a sectional view of a light emitting keypad having a lightguide film according to another embodiment of the present invention.

FIGS. 14 to 16 are sectional views of light emitting keypads havinglight guide films according to other embodiments of the presentinvention.

EXPLANATION OF REFERENCE NUMERALS FOR MAIN PORTIONS IN DRAWINGS

-   -   10: Light guide film 11: Reflection layer    -   12: Light source 13: Double-sided tape    -   14: Pattern 15: Adhesive member    -   20: Key 21: Protrusion    -   22: Key plate 23: Back layer    -   30: Substrate 31: Contact terminal    -   32: Metal dome

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

First, a light guide film for a keypad backlight according to thepresent invention will be explained.

FIGS. 3 to 5 are sectional views of a light guide film according to anembodiment of the present invention. The light guide film for a keypadbacklight is to allow light incident from a light source (12) to besurface-emitted and is characterized in that a reflection layer (11) isformed on a lower portion of the light guide film (10), and patterns(14) are locally formed in specific regions on at least one surface offront and back surfaces of the light guide film (10) so that light isintensively supplied to predetermined regions of the keypad.

As can be understood from the term, the light guide film (10) ischaracterized by a slim film, and preferably has a thickness in a rangeof 50 to 250 μm contrary to a conventional light guide plate. In case ofthe conventional light guide plate, the large thickness of theconventional light guide plate deteriorates a click feeling and iscontrary to a tendency to slimness of a light emitting keypad. The lightguide film has low light emitting efficiency if the thickness of thelight guide film is less than the thickness range, whereas a clickfeeling of the light guide film may be deteriorated and it may bedifficult to achieve slimness of the light guide film if the thicknessof the light guide film is greater than the thickness range.

The light guide film (10) is preferably made of a material that is slimand has a superior light guiding property and superior physicalproperties. The material is preferably selected from, but not limitedto, polycarbonate (PC) and polyethylene terephthalate (PET).

When the light guide film is a slim film as above, the light guide filmmay have lower light emitting efficiency as compared with a relativelythicker light guide plate. To solve this problem, it is preferred that areflection layer (11) for reflecting light, which may be lost, beprovided on a lower portion of the light guide film.

The material of the reflection layer (11) may be selected, withoutlimitation, from any materials so far as the materials can reflectlight, wherein a white pigment and the like can be used solely or in apaste form. It is preferred that the material of the reflection layer beat least one selected from silver (Ag), titanium dioxide (TiO₂), zincoxide (ZnO), barium sulfate (BaSO₄), zinc sulfide (ZnS), lead white andantimony oxide (Sb₂O₃).

The reflection layer may be formed on a back surface of the light guidefilm by a deposition method, a coating method, a printing method or thelike. Since the deposition method, the coating method and the printingmethod are well known, detailed descriptions thereof will be omitted.

As illustrated in FIGS. 4 and 5, the reflection layer is preferablyformed of a sheet containing a reflecting material and is morepreferably formed by attaching the sheet to one end or both ends or theentire of the back surface of the light guide film using a double-sidedtape (13).

The reflection layer may be in fully close contact with or spaced apartby a predetermined distance from the light guide film. A method ofcausing the reflection layer to be spaced apart by the predetermineddistance from the light guide film can be performed by bonding thereflection layer to one end or both ends of the light guide film using adouble-sided tape (13) with a predetermined thickness, as illustrated inFIG. 5. That is, when the reflection layer is bonded to only one end orboth ends of the light guide film, a predetermined gap corresponding tothe thickness of the double-sided tape is produced between thereflection layer and the light guide film at other portions of the lightguide film except the one end or both ends of the light guide film.

Once the reflection layer is lengthened than the light guide film andends of the reflection layer are then bonded to the light guide film, ifnecessary, the gap may be further increased as much as an excessivelength of the reflection layer. Particularly, since a substrate havingconvexo-concave dome switches is disposed below the light guide film incase of a light emitting keypad, it is also desirable to sufficientlylengthen the reflection layer such that the reflection layer can bedisposed to be in contact with the substrate having the dome switches.

When a gap is produced between the reflection layer and the light guidefilm, luminance of a light emitting keypad can be improved by allowingthe reflection layer to reflect light incident into the gap, therebyemitting the reflected light to the outside through the light guidefilm.

Furthermore, it is preferred that patterns (14) be locally formed inspecific regions on at least one of the front and back surfaces of thelight guide film in such a manner that light is intensively supplied topredetermined regions of the keypad. Emitted light is more concentratedin the regions formed with patterns than regions without the patterns.Since it is significant to cause light to be more concentrated intoregions of numeral or character keys in case of a keypad, it isdesirable to position the patterns to correspond to the key regions.

Although there is no limitation on a method of forming the patterns(14), it is desirable to use a hot press method. Since the light guidefilm of the present invention is a very slim film, it is not easy toform the patterns by means of injection molding. Furthermore, even incase of the hot press method, the light guide film may be damaged, forexample, thermally deformed if a mold heated to a high temperature isused. Therefore, it is desirable to use a mold heated to a temperaturein a range at which such damage is not produced. The patterns arepreferably formed, without being limited thereto, by means of the hotpress method using a mold heated to a temperature in a range of 70 to150° C.

On the other hand, the patterns may be formed by means of silk printingusing an ink containing a light scattering material on the light guidefilm.

MODE FOR THE INVENTION

FIGS. 6 and 7 are views showing examples of patterns of a light guidefilm for a keypad backlight according to other embodiments of thepresent invention. Although only the formation of concave patterns on alight guide film is shown, the present invention is not limited theretobut may include the formation of convex patterns. Light is refracted andscattered by the patterns so that light can be more efficiently emittedto a keypad.

FIGS. 8 to 10 are views showing examples of patterns (14) of a lightguide film for a keypad backlight according to other embodiments of thepresent invention. As shown in the figures, it is preferred that apattern is formed such that the pattern has a density increasing as thepattern goes far away from light sources, so as to provide a lightemitting surface enabling uniform light emission, which is similar tothat at a position closer to the light sources, even at a position faraway from the light sources. That is, since the amount of light suppliedfrom the light sources is reduced as the pattern goes away from thelight sources, the density of the pattern is increased so that light canbe scattered much more, thereby obtaining a more uniform light emittingsurface. The density of the pattern may be controlled by adjusting aninterval of the pattern, i.e., a pitch of the pattern (FIG. 8).Alternatively, the density of the pattern may be controlled by adjustingthe size of the pattern (FIG. 9). On the other hand, an intensive lightemitting surface may be provided instead of a uniform light emittingsurface by aggregating patterns densely in specific regions to providemore light emission to predetermined regions, e.g., character regions ona keypad (FIG. 10). The configurations of the patterns may be combinedwith one another. That is, patterns can be formed by combining theinterval adjustment, the size adjustment and the degree of concentrationwith one another. That is, the size of the pattern may be increased asthe pattern goes away from the light sources, as shown in FIG. 10.

The shape of the pattern (14) is not limited to a particular shape andthe present invention includes patterns formed through machining orprinting on a surface of a light guide plate.

A light emitting keypad according to the present invention will bedescribed below.

FIGS. 11 and 12 are sectional views of a light emitting keypad accordingto an embodiment of the present invention.

The light emitting keypad according to the embodiment of the presentinvention comprises a key plate with a plurality of keys (20) formedthereon; a back layer disposed below the key plate and having aplurality of protrusions (21) corresponding to all or some of the keys(the key plate (22) and the back layer (23) are briefly shown as asingle component in FIGS. 11 and 12, and thus, see FIG. 13 specificallyshowing the key plate and the back layer); a light guide film (10)formed below the back layer to cause incident light from a side lightsource to be surface-emitted; and a substrate (30) disposed below thelight guide film (10) and having dome switches (31, 32) formed atpositions corresponding to the positions of the protrusions (21),wherein the light guide film (10) is a slim film with a thickness in arange of 50 to 250 μm.

It is possible to use a light guide film (10) selectively employing thefeatures of the aforementioned light guide film. That is, a reflectionlayer (11) is formed on a lower portion of the light guide film (10),and patterns are locally formed in specific regions on at least one offront and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad.

There is no limitation on a method of positioning the reflection layer(11) on the lower portion of the light guide film (10), and thereflection layer may be bonded to the light guide film using an adhesive(FIG. 11) or a double-sided tape (13) (FIG. 12). Although not shown inthe figures, the reflection layer may be bonded to the light guide filmsuch that they are spaced apart from each other, as specificallydescribed above in connection with the light guide film.

The lower protrusions and the light guide film may be spaced apart fromeach other or brought into contact with each other as shown in thefigures.

The key plate (22) can be employed in the light emitting keypad withoutlimitation, and the present invention does not particularly restrict theshape and material of the key plate. That is, as shown in FIGS. 11 and12, each of keys of the key plate may be formed in a convex shape, in aconcave shape, or in a planar shape with a corresponding character ornumeral expressed thereon. Since the keys of the key plate are wellknown in the art, a detailed description thereof will be omitted.

If the keys are made of an integrally formed transparent flat sheet, thekeys can be expressed by printing an ink layer on a bottom surface ofthe key plate, and regions except the keys can be colored by forming acolored deposition layer in the regions.

The back layer (23) has the plurality of lower protrusions (21) and maybe formed integrally therewith without limitation. It is preferred thatthe back layer have excellent restoring force and be made of a materialsuch as silicone or polymer resin.

The plurality of lower protrusions (21) are preferably formed tocorrespond to the positions of all or some of the keys on the key plateof the light emitting keypad. When a user presses a key, a correspondinglower protrusion is pressed to make electrical connection in a switchingpart such as a dome switch placed below the light guide film.

Although there is no particular limitation on the light source (12), anLED is most preferred. The LED is proper since it can easily realizecolors and fabricated at low costs. The light source is disposed at aside end of the light guide film and thus becomes a side light source,wherein side light emitted from the light source is converted intosurface light by the light guide film.

The substrate (30) may be, but not limited to, a printed circuit board(PCB) and has dome switches each of which comprises a metal dome (32)and a contact terminal (31). Therefore, when a user presses a key top onthe keypad, a corresponding protrusion formed on the bottom of the keytop is pressed and elastically deforms a pressed region of the lightguide film so that a corresponding metal dome (32) of the printedcircuit board (30) is pressed and then brought into contact with thecontact terminal (31).

Although the metal domes can be formed separately as shown in FIG. 12,the metal domes may be formed of an integrally manufactured domesubstrate as shown in FIG. 13.

FIG. 13 is a sectional view of a light emitting keypad according toanother embodiment of the present invention. As shown in FIG. 13, thelight emitting keypad comprises a key plate (22) with a plurality ofkeys (20) formed thereon; a back layer (23) disposed below the key plate(22) and having a plurality of protrusions (21) corresponding to all orsome of the keys; a light guide film (10) formed below the back layer(23) to cause incident light from a side light source to besurface-emitted; and a substrate (30) disposed below the light guidefilm (10) and having dome switches formed at positions corresponding tothe positions of the protrusions, wherein a reflection layer (11) isformed on all or a portion of an upper surface of the substrate havingthe dome switches. Descriptions of parts overlapping with the foregoingdescription will be omitted.

The reflection layer (11) is preferably bonded to one side end of thelight guide film using an adhesion member (15), such as a double-sidedtape with a predetermined thickness, so that the light guide film andthe reflection film are spaced apart by a predetermined distance fromeach other, as shown in the figure. Furthermore, although notillustrated in the figure, the reflection layer may be bonded to bothside ends of the light guide film or may be formed, separately from thelight guide film, on all or a portion of an upper surface of thesubstrate having the dome switches.

The light guide film may selectively have the features of theaforementioned light guide film if necessary. As preferred examples, thelight guide film is a slim film with a thickness in a range of 50 to 250μm, and patterns are locally formed in specific regions on at least oneof front and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad.

FIGS. 14 to 16 are sectional views of light emitting keypads accordingto other embodiments of the present invention. As shown in the figures,the light emitting keypad comprises a key plate (22) with a plurality ofkeys (20) formed thereon; a light guide film (10) disposed below the keyplate to cause incident light from a side light source to besurface-emitted; a plurality of protrusions (21) formed at predeterminedpositions below the light guide film; and a substrate (30) disposedbelow the protrusions and having dome switches formed at positionscorresponding to the positions of the protrusions, wherein the lightguide film (10) is a slim film with a thickness in a range of 50 to 250μm. Descriptions of parts overlapping with the foregoing descriptionwill be omitted. A back layer (23) shown in FIG. 16 may be eliminated,if necessary.

The light guide film may selectively have the features of theaforementioned light guide film if necessary. That is, a reflectionlayer (11) is formed on a lower portion of the light guide film (10),and patterns are locally formed in specific regions on at least one offront and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad. There is nolimitation on a method of positioning the reflection layer (11) on thelower portion of the light guide film (10), and the reflection layer maybe bonded to the light guide film using an adhesive (FIG. 14) or adouble-sided tape (13) (FIG. 15). Although not shown in the figures, thereflection layer may be bonded to one side end of the light guide filmusing a double-sided tape with a predetermined thickness such that theyare spaced apart from each other, as specifically described above inconnection with the light guide film.

In such configurations, the protrusions (21) are formed on the lowerportion of the light guide film rather than an upper portion of thelight guide film (10). The formation of the protrusions on the upperlower portion of the light guide film reduces a possibility ofoccurrence of a problem with reliability of the keypad, which is causedby deformation of the light guide film and the patterns formed on thelight guide film due to pressing of the protrusions if the protrusionsare formed on the upper portion of the light guide film.

The protrusions (21) may be made of a material selected from siliconeand a polymer resin.

As for a method of forming the protrusions (21), the protrusions may beformed directly on the light guide film, or formed by attaching a layerwith the protrusions formed therein to the back surface of the lightguide film. The method of forming the protrusions includes, but notlimited to, press molding of liquid silicone or film silicone, a polymerresin, or the like at 100 to 150° C. using a mold formed to correspondto the protrusions (21); photolithography; and screen printing using anUV-curing or an IR-curing ink.

Since the aforementioned embodiments are not for limiting the presentinvention but for specifically describing the present invention,changes, modifications and elimination made thereto within the technicalspirit of the present invention are included in the scope of the presentinvention defined by the appended claims.

INDUSTRIAL APPLICABILITY

With the light guide film for a keypad backlight and a light emittingkeypad comprising the light guide film according to the presentinvention, substantial slimness is achieved as compared with a directillumination type keypad, high luminance is obtained by introducing areflection layer even though a small number of light sources are used,and a light emitting surface can be provided for intensive lightemission onto key regions of a keypad by forming a predetermined patternon at least one surface of the light guide film. Particularly, the lightguide film and the light emitting keypad according to the presentinvention are properly applicable to mobile terminals.

1. A light emitting keypad comprising: a key plate with a plurality ofkeys formed thereon; a back layer disposed below the key plate andhaving a plurality of protrusions corresponding to all or some of thekeys; a light guide film formed below the back layer to cause incidentlight from a side light source to be surface-emitted; and a substratedisposed below the light guide film and having dome switches formed atpositions corresponding to the positions of the protrusions, wherein thelight guide film is a slim film with a thickness in a range of 50 to 250μm.
 2. The light emitting keypad as claimed in claim 1, wherein areflection layer is formed on a lower portion of the light guide film,and patterns are locally formed in specific regions on at least one offront and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad.
 3. Thelight emitting keypad as claimed in claim 1, wherein the light guidefilm is made of polycarbonate (PC) or polyethylene terephthalate (PET).4. A light emitting keypad comprising: a key plate with a plurality ofkeys formed thereon; a back layer disposed below the key plate andhaving a plurality of protrusions corresponding to all or some of thekeys; a light guide film formed below the back layer to cause incidentlight from a side light source to be surface-emitted; and a substratedisposed below the light guide film and having dome switches formed atpositions corresponding to the positions of the protrusions, wherein areflection layer is formed on all or a portion of an upper surface ofthe substrate having the dome switches.
 5. The light emitting keypad asclaimed in claim 4, wherein the light guide film is a slim film with athickness in a range of 50 to 250 μm, and patterns are locally formed inspecific regions on at least one of front and back surfaces of the lightguide film so that light is intensively supplied to predeterminedregions of the keypad.
 6. A light emitting keypad comprising: a keyplate with a plurality of keys formed thereon; a light guide filmdisposed below the key plate to cause incident light from a side lightsource to be surface-emitted; a plurality of protrusions formed atpredetermined positions below the light guide film; and a substratedisposed below the protrusions and having dome switches formed atpositions corresponding to the positions of the protrusions, wherein thelight guide film is a slim film with a thickness in a range of 50 to 250μm.
 7. The light emitting keypad as claimed in claim 6, wherein areflection layer is formed on a lower portion of the light guide film,and patterns are locally formed in specific regions on at least one offront and back surfaces of the light guide film so that light isintensively supplied to predetermined regions of the keypad.
 8. A lightguide film for a keypad backlight to cause incident light from a lightsource to be surface-emitted, the light guide film comprising: areflection layer formed on a lower portion thereof, wherein patterns arelocally formed in specific regions on at least one of front and backsurfaces of the light guide film so that light is intensively suppliedto predetermined regions of the keypad; wherein the light guide film isa slim film with a thickness in a range of 50 to 250 μm.
 9. The lightguide film as claimed in claim 8, wherein the light guide film and thereflection layer are spaced apart by a predetermined distance from eachother.
 10. The light guide film as claimed in claim 8, wherein thereflection layer is formed of a sheet and attached to one side end, bothside ends or the entire of the back surface of the light guide filmusing a double-sided tape.
 11. The light guide film as claimed in claim8, wherein the patterns are formed by means of a hot press method usinga mold heated to a temperature in a range of 70 to 150° C.
 12. The lightguide film as claimed in claim 8, wherein the patterns are formed bymeans of silk printing using an ink containing a light-scatteringmaterial on the light guide film.
 13. The light guide film as claimed inclaim 8, wherein the patterns have sizes increasing as the patterns goaway from the light source.